When treating a runner with a suspected stress reaction or stress fracture, there is often a relative urgency to rule out stress fracture or stress reactions because the runner has an impending race. When bone stress injury is suspected, the standard diagnostic/treatment algorithm of “avoid stressing the tissue for 3-4 weeks, gradually return to running and possibly repeat x-rays” is not met with great enthusiasm from the runner patient. They want to get out and run ASAP. Therefore, early diagnosis is very important.
MRI is still the gold standard for diagnosing stress injuries to bones (bone marrow edema, stress fractures, periosteal reactions), however it remains very expensive.
Therapeutic ultrasound (TUS) is a useful, much less expensive tool in the clinician’s toolbox to help diagnose higher grade stress injuries to bone. In a 2012 study, researchers compared TUS to MRI for picking up stress injuries. When compared to MRI, TUS had a 95% sensitivity in positively diagnosing patients with high grade stress injuries and 84% accuracy. However, it was not very good at picking up lower grade bone stress injuries. The classic Fredericson grade system is shown below.
In addition to the TUS, there is some limited evidence (Lesho, 1997) that application of a tuning fork to the injured site is helpful in detecting stress fractures.
The use of plain film X-rays is of limited value. Matheson et al., 1987 found x-rays can only pick up stress fractures 10% of the time initially, but Ishibashi et al., 2002 found that the sensitivity gradually increases it’s sensitivity to 30-70% over the course of 3 weeks. This is due to the ability of the x-rays to image the healing bone.
In the end, the clinician needs to piece together all of the signs and symptoms in order to complete the clinical picture and make a rational decision. When taken in isolation, the TUS, x-rays, tuning fork, clinical exam and history are not enough to go by. When all these are taken into account (along with the goals and needs of the runner), the clinician should then make a decision whether or not to go ahead with the use of more expensive CT, bone scan or MRI.